1. Field of the Invention
The present invention relates to a magnetic disc into and/or from which an information is written and/or read by a magnetic head installed on a head slider, and a magnetic disc drive in which the magnetic disc is usable.
2. Description of Related Art
Conventionally, the conventional magnetic disc used in the magnetic disc drive has a magnetic film formed on either side of the magnetic disc to cover the entire disc surface. To suppress a cross-talk from neighboring tracks, the guard band between the recording tracks has to be wider. Thus, in the conventional magnetic disc, it is difficult to form the tracks at a reduced pitch, Therefore, the conventional magnetic disc cannot be designed more compact and to have a larger storage capacity.
To overcome the above drawbacks of the conventional magnetic disc, the Applicant of the present invention proposed an improved magnetic disc and a magnetic disc drive in which the magnetic disc is usable (in the Japanese patent application laid open as a Provisional Publication No. 259709/'94).
The magnetic disc disclosed in this Japanese patent application laid open as a Provisional Publication No. 259709/'94 has a zone in which information is recorded (will be referred to as "data zone" hereinunder) and a zone in which control signals including servo signal are recorded (will be referred to as "servo zone" hereinunder).
Referring now to FIG. 1, there is schematically illustrated the above-mentioned magnetic disc, generally indicated with a reference 200, having data zones 300 in which lands 300a are formed as data recording tracks and a groove 300b is formed as a guard band between two neighboring recording tracks.
As shown in FIG. 1, the magnetic disc has also a servo zone 400 formed from lands 400a (will be referred to as "servo pits" hereinunder) corresponding to a control signal such as servo signal, etc. In the servo zone 400, the lands 400a are magnetized to have one polarity and the grooves 400b are magnetized to have an opposite polarity, for writing a servo signal before the magnetic disc is used for data recording and reproduction. The grooves 400b provide a reference plane.
The above magnetic disc 200 has guard bands physically formed as grooves in relation to the recording tracks, so cross talk will not easily occur. Therefore, since the guard bands have not to be wider to suppress cross talk, the track pitch may be smaller to have a larger recording capacity of the magnetic disc 200. As the track pitch can be smaller, a more higher density of recording can be attained.
The servo pits 400a, lands, can easily be formed extremely fine and highly accurately in the magnetic disc 200. By pre-forming servo pits correspondingly to a control signal, the control signal can be written into the magnetic disc 400 very accurately.
Namely, since a control signal can be written in a very precise position relative to the recording track, data can easily be recorded on the magnetic disc 200 more densely than in a conventional magnetic disc in which no servo pits are formed.
However, when a head slider is used for data read/write from/into the magnetic disc 200 having such a high recording density, the head slider has to be designed to float about 50 nm or less, for example, in order to minimize the spacing loss.
The variation of floating height must also be smaller because the spacing loss is caused not only by the floatation but also by its variation.
As shown in FIG. 1, however, the servo and data zones 400 and 300 in the magnetic disc 200 in which the above-mentioned servo pits 400a are pre-formed are different in pattern form from each other. Therefore, the head slider floats to a different height in the servo zone 400 from it does in the data zone 300. The difference in floating height from one zone to another causes the head slider to float at various heights, so the magnetic head installed on the head slider cannot stably record and reproduce information signal.
For the magnetic disc 200, a following method has been studied for minimizing the variation of floating height of the head slider in passing over the servo zone to assure a stable information recording and reproduction.
Namely, the pattern in the servo zone is designed, by making the track-directional length of the servo zone smaller than a predetermined value, for example, to minimize the variation of floating height of the head slider passing over the servo zone.
Normally, the pattern in the servo zone is designed for improvement of the accuracy of magnetic head positioning. Thus, the pattern in the servo zone to inhibit the variation of head slider floating can be designed with a limited freedom, resulting in a sacrifice of the accuracy of magnetic head positioning which is the most important.